Lord Turner, the chairman of the Financial Services Authority (FSA), has placed himself on a collision course with the former directors of Royal Bank of Scotland (RBS) by refusing to bow to objections over criticisms of their conduct at the crisis-hit lender.I can reveal that Lord Turner is expected to say in his foreword to the report on RBS's failure, which will be published on Monday, that the bank conducted due diligence ahead of its £49bn takeover of ABN Amro which "amounted to two lever-arch files and a CD-ROM".I'm told that some of RBS's former directors, whose lawyers have scrutinised the report, have objected to the claim on the basis that it is inaccurate and misleading.But my sources tell me that Lord Turner has refused to budge and that the phrase will remain in the final report.In one sense, the wording should be uncontroversial: Sir Fred Goodwin, the boss of RBS at the time of the ABN deal, said publicly that he wanted a "due diligence-light" approach to the takeover because of the lack of time available to the bank.At the time, Goodwin cited Barclays' own extensive due diligence as a reason for RBS not to need to replicate it. That view turned out to be disastrously misguided as ABN's exposure to toxic assets in the US sub-prime mortgage turned out to be gargantuan.Nonetheless, it does seem that Turner's characterisation is deliberately provocative and given the weight that his words carry as the chairman of the City regulator, it might be argued that he is heightening the exposure of those former directors to the risk of litigation.It's also the case, as I have mentioned before, that the report acknowledges that ABN was a bank regulated by some of the most rigorous financial regulators in the world - and if the due diligence carried out by RBS's board was inadequate, that also raises profound questions about the quality of the FSA's own supervision of the bank.Neither the FSA nor RBS would comment.